1. Technical Field
The present invention relates to a process for producing corn-based pellets and, in particular, to a process providing precise control of the processed corn cook level, moisture level, gelatinization and resultant product quality despite variations in the characteristics of the starting meal. The invention manipulates steam and water addition in the preconditioner and either water addition and rotation speed or residence time and screw configuration in the extruder in order to achieve the appropriate processed meal characteristics at each stage.
2. Description of Related Art
The process for producing pellets as generally adapted in the food industry involves a very minimal cook of starch and forming a shape, such as a particular pasta shape, wherein the product is later cooked in the presence of excess water. Alternatively, cooked meal, such as pressure-cooked corn meal, can be used. The cooked mass is sheeted, cut, and dried for later frying.
Processes for producing corn-based pellets for use as a snack food product are well known in the art. For example, U.S. Pat. No. 3,348,950 to Weiss describes a process for making snack food product by first mixing together corn, sucrose, water, and flavor developing ingredients. This mixture is combined with a second mixture of yellow corn grits, water, and sodium bicarbonate. The combined mixture is pre-cooked under pressure of 14 to 20 psi and temperatures between 119 and 127.degree. C. The gelatinized dough is shaped, dried, and formed into pieces for deep-fat frying.
The method disclosed by the Weiss patent is a common process for producing corn meal based pellets that are fried and flavored. Common industry methods, however, are not adequate for the production of a corn-based pellet that expands or pops when fried to produce a light, crispy, and crunchy corn snack. For the purposes of this disclosure, an expanded pellet is one that increases in volume by upwards of 100% due to the rapid vaporization of water within the pellet during rapid heating of the pellet by, for example, deep frying.
Known methods for producing corn-based pellets do not provide the means for precisely controlling the cook level and degree of gelatinization at each stage in order to compensate for minor variations in the characteristics of the starting meal while at the same time inhibiting microbial growth by keeping all related processing temperatures high. When using prior art techniques at higher mixing temperatures, minor variations in the quality of the starting corn flour meal can result in dramatic variations in the quality of the end product.
For example, conventional pellet production teaches extruding pellets after a relatively cool (around 49.degree. C.) and long (8-15 minutes) preconditioning step that presents a homogenous hydrated mixture to the extruder with approximately 33% moisture. A disadvantage of the relatively cool temperature used during the preconditioning step is that it fosters microbial growth and requires frequent sanitation of the preconditioner. Conventional extrusion takes place at between 240 to 250 rpm with no water injection into the extruder. Raising the temperature of this process using prior art methods in order to counteract microbial growth results in a product that is overcooked. This typically results in the production of an unacceptable amount of "flats," which are pellets that did not appropriately expand when fried. The use of conventional processing methods at increased preconditioner temperatures also results in a process that is extremely sensitive to variations in the characteristics of the starting meal.
Accordingly, a need exists for a process for expanded pellet production that provides for precise control of cook level, hydration, gelatinization, and quality of the product in order to produce a uniform expanded corn-based snack while also maintaining elevated processing temperatures in order to control microbial growth and limit associated equipment downtime. This process should also be adaptable for use with traditional corn-based pellets that exhibit less expansion upon frying or other means of re-thermalization.